Generally, a direction perpendicular to a p-n junction of a semiconductor laser device is referred to as a fast axis, whereas a direction in parallel to the p-n junction is referred to as a slow axis. A numerical aperture of a semiconductor laser device in a direction along its fast axis is much greater than that in a direction along its slow axis. Therefore, a laser beam emitted from a semiconductor laser device greatly spreads in a direction along its fast axis. Accordingly, a collimator lens for collimating fast-axis components of a laser beam emitted from a semiconductor laser device should be arranged near an emitting surface of the semiconductor laser device (see, e.g., Patent Literature 1 and Patent Literature 2).
In order to arrange a desired optical system using such a collimator lens, it is necessary to fix the collimator lens highly precisely relative to a semiconductor laser device in a direction parallel to an optical axis and a direction parallel to a fast axis and to prevent variations in positional relationship between the semiconductor laser device and the collimator lens. Specifically, the positional relationship between the semiconductor laser device and the collimator lens should be fixed and maintained in the micron order.
For example, in an optical fiber attachment apparatus disclosed in FIG. 4 of Patent Literature 1, a collimator lens (optical fiber lens 26) is attached so that it can slide along its axis. In order to attach the optical fiber lens 26 in a slidable manner, a certain clearance needs to be formed between a cylindrical clamp 52 and the optical fiber lens 26. Therefore, variation in position of the optical fiber lens 26 cannot be reduced in the micron order in both of a direction of an optical axis of a laser beam emitted from a semiconductor laser device bar 10 and a direction along a fast axis.
Furthermore, the optical fiber lens 26 of Patent Literature 1 is fixed to an attachment member 40 with an epoxy resin 50. The optical fiber lens 26 is deviated in the direction of the optical axis of the laser beam by shrinkage of the epoxy resin 50 on curing. Moreover, since the optical fiber lens 26 is fixed directly to the attachment member 40 with the epoxy resin 50, the amount of the epoxy resin 50 that is not less than required for alignment needs to be provided between the attachment member 40 and the optical fiber lens 26 in order to conduct alignment of the optical fiber lens 26. The optical fiber lens 26 is also deviated in a direction along its fast axis by shrinkage or expansion of the epoxy resin 50 due to a temperature change or a humidity change.
Furthermore, Patent Literature 2 discloses a semiconductor laser module in which a semiconductor laser device 1 and a collimator lens 6 are fixed to one supplementary member 4 with brazing layers 5 and 8, respectively, to reduce variations in positional relationship between the semiconductor laser device 1 and the collimator lens 6 in cooperation with deflection of the semiconductor laser device 1 and deflection of the collimator lens 6. When the position of the semiconductor laser device 1 is adjusted, the semiconductor laser device 1 needs to be positioned at a high temperature of, for example, about 400° C. in order to braze the brazing layers 5 and 8. However, a laser beam cannot be emitted from the semiconductor laser device 1 at such a high temperature. Thus, there is a problem that the collimator lens 6 cannot be aligned while a laser beam is emitted from the semiconductor laser device 1 (what is called active alignment cannot be performed).
In this case, active alignment can be performed if the semiconductor laser device 1 and the collimator lens 6 are fixed with a resin or the like instead of the brazing layers 5 and 8. In such a case, however, the position of the supplementary member 4 and the collimator lens 6 greatly varies relative to the semiconductor laser device 1 due to shrinkage or expansion of the resin. Accordingly, there is a problem that the collimator lens 6 is deviated from the aligned position.